1. Field of the Invention
The present invention relates to a thermal head and a printer.
2. Description of the Related Art
There has been conventionally known a thermal head for use in printers, in which an intermediate layer is provided between a support substrate and an upper substrate and the intermediate layer has a cavity portion formed therein in a region corresponding to heating resistors (see, for example, Japanese Patent Application Laid-open No. 2007-83532).
In the thermal head disclosed in Japanese Patent Application Laid-open No. 2007-83532, the cavity portion formed in the intermediate layer functions as a heat-insulating layer of low thermal conductivity to reduce an amount of heat transferring from the heating resistors toward the support substrate, to thereby increase thermal efficiency and reduce power consumption.
In the thermal head disclosed in Japanese Patent Application Laid-open No. 2007-83532, when the support substrate is formed of a material having good thermal conductivity, such as silicon, ceramics (alumina), or a metal (aluminum or copper), in order to increase the thermal efficiency of the thermal head, the intermediate layer needs to have a certain degree of thickness for suppressing the heat dissipation toward the support substrate.
However, if the thickness of the intermediate layer is too large, the heat dissipation effect toward the support substrate is significantly reduced to raise a temperature of the upper substrate excessively, resulting in low printing quality. Therefore, in order to suppress the heat dissipation toward the support substrate while maintaining the printing quality, the thickness of the intermediate layer needs to be about several tens μm to 100 μm.
However, in the case of forming the intermediate layer by screen printing using a glass paste, there is an inconvenience that a glass thickness obtained after baking may be as small as about 5 μm to 20 μm. Alternatively, in the case of forming the intermediate layer by photolithography using a polymer resin, because the intermediate layer is soft and has a large coefficient of thermal expansion, there is an inconvenience that the intermediate layer may be transformed due to continuous heating or that a bonding force to the upper substrate may reduce due to thermal stress.